The invention relates to lifting apparatus comprising a mast and a load engaging mechanism moveable vertically along the mast. More particularly, the invention relates to brake mechanisms for preventing either the operator's cab or the load of such an apparatus from accidentally dropping. Still more particularly, the invention relates to stacker cranes.
A conventional stacker crane has a bridge moving along a runway, and a trolley moving along the bridge. The trolley includes a frame and a turntable rotatable relative to the frame about a vertical axis. A conventional stacker crane also includes a mast assembly depending vertically from the turntable. The mast assembly includes an upper or rigid mast depending from the turntable, and an intermediate mast moveable vertically along the rigid mast. An operator's cab is mounted on the intermediate mast for housing an operator controlling the stacker crane. A carriage is moveable vertically relative to the intermediate mast. A load engaging mechanism, such as a pair of forks, moves with the carriage. The carriage is raised and lowered by a hoist assembly on the trolley.
A stacker crane typically includes a brake mechanism for preventing undesirable or uncontrolled downward movement of the operator's cab or the load relative to the rigid mast. A brake mechanism on the intermediate mast includes a brake member which is supported by a housing mounted on the intermediate mast and which engages the rigid mast to prevent downward movement of the intermediate mast relative to the rigid mast. An overspeed mechanism causes the brake member to engage the rigid mast when the downward velocity of the intermediate mast relative to the rigid mast exceeds a predetermined value.